The recent emphasis placed on recycling of industrial products has created a need for new separation technologies in the recycling industry. This is particularly true for the scrap metal industry. Predominant areas of interest include iron and steel, aluminum and copper. Unlike the others, copper presents a somewhat more challenging problem since a significant by-product (plastic insulation) is generated by the recycling of scrap wire.
Current practice for recovery of copper from used or scrap wire involves shredding followed by screening to separate the wire from the plastic insulation. Although this approach is quite effective at recovering 80-90% of the wire, a substantial portion of copper and/or aluminum is lost with the plastic reject material. This is a result of inefficiencies in both the shredding and screening procedures.
More recently, standard mineral processing separation procedures have been applied to recover the misplaced wire. This approach involves the use of electrostatic separation to recover the lost metallics from the plastic reject stream. Unfortunately, this technique is only applicable to dry, free-flowing material. As a result, separation of material which has been stock-piled outdoors for an extended period of time is not feasible.
The incentive to develop a new process for recovery of valuable metallics from stock-piled waste is two-fold. First, and most important, the exposure of heavy metals, such as copper, to weathering conditions creates an environmental hazard with regard to ground water contamination. This hazard also eliminates landfilling as an alternative for disposal of the waste plastics. Second, the amount of metallics present in these stock-piles represents a substantial source of income, if this material can be effectively recovered. Likewise, the potential also exists to generate a clean plastic by-product which may be marketable.
It is an object of this invention to provide a novel process for the recovery of plastic and of metal from waste scrap containing these two values. It is another object of this invention to provide a novel process for stripping plastic insulation material from waste scrap wire and for recovering the metal values and the insulation material values as separate, substantially pure products. Still other objects will appear from the following detailed description.